Objective: Instruments for auditory assessment or sound analysis were conventionally used to evaluate abnormal speech sounds. However, since the representations by these subjective or objective methods are ambiguous and difficult to understand, they are not practical for feedback to patients in speech therapy. The purpose of this study was to analyze the articulation patterns of patients with mandibular prognathism using our speech visualization system and to evaluate the usefulness of this system.
Subjects and Methods: The study group comprised 7 patients with mandibular prognathism who had undergone orthognathic surgery with glossectomy in our department (patient group) and 21 subjects with normal occlusion (normal group). All subjects pronounced 100 syllables containing the five Japanese vowel sounds and 50 words for assessment of articulation in a soundproof chamber, and the speech signals were converted into WAV-formatted digital data. In the speech intelligibility test, the 100-syllable recordings of the patient group were evaluated preoperatively and postoperatively by 5 listeners with normal hearing. Furthermore, the articulation pattern of the 50-word speech data was analyzed using our speech visualization system. In this system, the first, second, and third formant frequencies were converted into three primary colors, and the phoneme features of vowel sounds were represented as unique colors. At the same time, we designed a horizontal-vertical (hv) articulation diagram to represent the speaker's articulatory status, and compared the patients' distributions with normal ones as control. Moreover, the degree of distortion from the control distribution was quantified using a vowel balance chart. Using these visualization and quantification methods, we investigated the articulation changes of the patient group preoperatively and postoperatively and the differences between the two groups.
Results: In the speech intelligibility test, speech intelligibility scores of the patients improved in postoperative recordings. In the hv articulation diagram, the distribution pattern of vowel sounds of the patients approached that of the control subjects postoperatively since some of the vowel sounds of the patients distributed outside of the normal range in preoperative recordings fell in the normal range in postoperative recordings. In the vowel balance chart, the pattern of the patients in postoperative recordings improved and was nearly similar to that of the control subjects.
Conclusion: Speech visualization systems can be a useful tool for articulation pattern analysis in patients with mandibular prognathism.
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